Novel lectin-related proteins are major components in lima bean (Phaseolus lunatus L.) seeds

Cloning, expression and characterization of arcelin and its impact on digestive enzymes of the stored product insect pest, Callosobruchus maculatus (F.)

The pulse beetle Callosobruchus maculatus causes potential damage to legume crops by infesting the seeds, leading to a reduction of total protein content. Arcelin found in the wild accessions of the common bean, is an insecticidal protein that has the potency to hamper the metabolism of the bruchid beetle. The arcelin gene from the wild accession of Phaseolus lunatus was isolated and the ORF encoding 158 amino acids was cloned in pET-45b (+) vector. The recombinant clones were transformed in BL21 STAR (DE3) pLysS cells, and the expressed arcelin was purified using Ni-NTA column. The recombinant protein was used in preparing an artificial diet, and the insecticidal activity was elucidated against the bruchid pest C. maculatus. Adult emergence and seed damage were drastically reduced in the treated groups. The response towards ingested diet by digestive enzymes involved in metabolism was elucidated through quantitative gene expression. The highest expression was observed in the aminopeptidase, followed by upregulation of alpha-amylase, glycoside hydrolase family 31 and cathepsin D-like aspartic protease, and downregulation of cathepsin L-like cysteine protease. The recombinant arcelin demonstrates effective insecticidal activity against the bruchid beetle. The changes in digestive enzymes to counteract the anti-nutritional nature of the protein were the strategies of the insect defense mechanism.

Lectin from seeds of a Brazilian lima bean variety (Phaseolus lunatus L. var. cascavel) presents antioxidant, antitumour and gastroprotective activities

Lectins are proteins able to interact specifically and reversibly with carbohydrates. They are present in all living beings, particularly in legume seeds, which have many biological functions. The aim of this study was to isolate, characterize and verify antioxidant, anti-hemolytic, antitumor and gastroprotective activities in a lectin present in seeds of Phaseolus lunatus L. var. cascavel (PLUN). The isolation of lectin was performed by size exclusion chromatography on Sephadex G-100, which was isolated from a protein capable of agglutinating only human erythrocytes type A, being this the only inhibited haemagglutination n-acetyl-d-galactosamine. Its weight was estimated by PAGE is 128kDa. The lectin is thermostable up to 80°C and is active between pH 2-11. As 8M urea was able to denature the lectin. PLUN is a glycoprotein consisting of 2% carbohydrate and has antioxidant action with ascorbic acid equivalent antioxidant capacity (μMAA/g) of 418.20, 326 and 82.9 for total antioxidant activity, ABTS radical capture and capture of DPPH radical, respectively. The lectin has antitumor activity against melanoma derived cells at doses of 100 and 50mg/ml, reducing up to 83% tumor cells, and gastroprotective action, reducing up to 63% damaged area of ​​the stomach induced by ethanol.

'Fagiolo a Formella', an Italian lima bean ecotype: biochemical and nutritional characterisation of dry and processed seeds

BACKGROUND

An ecotype of the lima bean, named 'fagiolo a Formella', which, to the best of our knowledge, is the only example of an Italian lima bean (Phaseolus lunatus L.) ecotype, is cultivated in the Campania region of southern Italy. Physical, nutritional and processing traits of dry seeds were evaluated for two consecutive growing seasons (2009 and 2010). The canning quality was also investigated, but only for the harvest of 2010.

RESULTS

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of total seed proteins allowed the attribution of 'fagiolo a Formella' to the Mesoamerican gene pool and Sieva morphotype. Seeds have a trapezoid shape, white coat and 100-seed weight greater than 42 g. Yield, protein, trypsin inhibitor and phytic acid values were found comparable with those reported for lima bean varieties cultivated in sub-tropical areas. Moreover, we found that this ecotype is devoid of lectin.

CONCLUSIONS

The good adaptation to growing environment is indicated by the fact that 'fagiolo a Formella' seed quality is comparable to that of lima beans grown in America. Overall the canning quality was found satisfactory and canning significantly destroys the main anti-nutritional compounds present in dry seeds.

Evolutionary analysis of the APA genes in the Phaseolus genus: wild and cultivated bean species as sources of lectin-related resistance factors?

The APA (Arcelin/Phytohemagglutinin/alpha-Amylase inhibitor) gene family is composed of various members, present in Phaseolus species and coding for lectin and lectin-related seed proteins having the double role of storage and defense proteins. Here members of the APA family have been identified by immunological, functional, and molecular analyses and representative genes were sequenced in nine wild species of Phaseolus. All taxa possessed at least one member of the true lectin gene. No arcelin type sequences have been isolated from the species examined. Among the wild species studied, only P. costaricensis contained an alpha-amylase inhibitor (alpha-AI). In addition P. augusti, P. maculatus, P. microcarpus, and P. oligospermus showed the presence of the lectin-related alpha-amylase inhibitor-like (AIL) genes and alpha-AI activity. Data from Southern blot analysis indicated the presence of only one lectin gene in P. parvulus and P. filiformis, while an extensive gene duplication of the APA locus was found in the other Phaseolus species. Phylogenetic analysis carried out on the nucleotide sequences showed the existence of two main clusters and clearly indicated that lectin-related genes originated from a paralogous duplication event preceding the development of the ancestor to the Phaseolus genus. The finding of detectable alpha-AI activity in species containing AIL genes suggests that exploiting APA genes variability in the Phaseolus genus may represent a valuable tool to find new members that may have acquired insecticidal activities.

Identification and isolation of lectin nucleotide sequences and species relationships in the genus Lens Miller

Genes for lectin, a component of legume storage proteins, were identified and characterised in two lentil cultivars ( Lens culinaris ssp. culinaris) and six wild relatives. In each taxon no differences were found among the two or three lectin clones sequenced, while differences were observed among lectin genes isolated from the different taxa. All of the clones analysed contained an insert of 828 bp and showed a high similarity with the nucleotide sequence of Pisum sativum seed lectin, PSL1. The deduced amino acid lectin sequences in all taxa were 275 amino acids long, and their multiple alignment showed that most of the variation among them occurred in regions which are not important for metal- and sugar-binding. The data from Southern blot analysis indicated the presence of only one lectin gene in all Lens taxa except L. tomentosus. Phylogenetic analyses carried out on the lectin sequences showed the existence of two main clusters and clearly indicated that L. nigricans falls outside the two groups.

Misfolding and aggregation of vacuolar glycoproteins in plant cells

Phaseolin and lectin-related polypeptides, the abundant oligomeric glycoproteins of bean seeds, are synthesized on the endoplasmic reticulum (ER) and then transported to the storage vacuole via the Golgi apparatus. Glycosylation and folding are among the major modifications these proteins undergo in the ER. Although a recurrent role of N-glycosylation is on protein folding, in previous studies on common bean (Phaseolus vulgaris) seeds we demonstrated that the oligosaccharide side-chains are not required for folding, intracellular transport and activity of storage glycoproteins. We show here that in lima bean (Phaseolus lunatus), incubation of the developing cotyledon with tunicamycin to prevent glycosylation has a dramatic effect on the intracellular transport of the storage glycoproteins. When lacking their glycans, phaseolin and lectin-related polypeptides misfold and are retained in the ER as mixed aggregates to which the chaperone BiP irreversibly associates. The lumen of the ER becomes enlarged to accommodate the aggregated polypeptides. Intracellular transport of legumin, a naturally unglycosylated storage protein, is mostly unaffected by the inhibitor, indicating that the observed phenomenon specifically occurs on glycoproteins. Furthermore, recombinant lima bean phaseolin synthesized in tobacco protoplasts is also correctly folded and matured in the presence of tunicamycin. To our knowledge, this is the first report that describes in detail the block of intracellular transport of vacuolar glycoproteins in plant cells due to aggregation following glycosylation inhibition.